2021–22 Thai League 3 National Championship

The National Championship was the next stage from the regional stage of 2021–22 Thai League 3. The winners and runners-ups of each region would qualify for this round to find 3 clubs promoting to 2022–23 Thai League 2.

Knockout stage
Winners, runners-up, and third place of 2021–22 Thai League 3 would be promoted to the 2022–23 Thai League 2.

Summary



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Matches
Nakhon Si United won 4–3 on aggregate.

Summary



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2nd leg
Uthai Thani won 3–1 on aggregate.

Teams promoted to 2022–23 Thai League 2

 * Uthai Thani (champions)
 * Krabi (runners-up)
 * Nakhon Si United (third-placed)